Tonescales for geographically localized digital rendition of people

ABSTRACT

In a method and system for processing a photographic image having lightness values, L*, representing one of the colorimetric values of an original scene, the photographic image is transformed. The transformed image has a gamma as a function of CIE 1976 L*, which includes a dark region having a rising slope, a light region having a falling slope, and a plateau region having a slope constantly within 5 percent of a maximum value in said plateau region. The rising slope is at least twice as large as the absolute value of the falling slope. The plateau region is between 10 L* and 30 L* wide. Gamma is a derivative of visually perceived reproduced CIE 1976 L* versus scene CIE 1976 L*. Gamma has a maximum slope between 1.5 and 2.0.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/899,756, filed Jul.27, 2004.

FIELD OF THE INVENTION

The invention relates to digital image processing and enhancement andmore particularly relates to methods and apparatus directed totonescales for geographically localized digital rendition of people.

BACKGROUND OF THE INVENTION

It has long been recognized that the rendition of people is one of themost important aspects of color rendition. Consequently, a significantamount of research has been done in the field of the optimum color andtone reproduction of skin tones (D. L. MacAdam, Proc. I. R. E., 42,1954, 166; R. W. G, Hunt, I. T. Pitt, L. M. Winter, “The PreferredReproduction of Blue Sky, Green Grass and Caucasian Skin in ColourPhotography”, J. Photogr. Science 22, 144, 1974; M. Yamamoto, Y-H Lim,X. Wei, M. Inui, H. Kobayashi, “On the Preferred Flesh Colour in Japan,China and South Korea”, The Imaging Science Journal, 51, 163, 2003).This literature indicates that preferences for the rendition of skintones may differ by geographic region, ethnic and cultural backgroundand skin type. (Also see the discussion of light and dark skin tones inU.S. Pat. No. 6,396,599 B1, to Patton et. al., entitled “Method andApparatus for Modifying Portions of an Image in Accordance withColorimetric Parameters (hereafter “Patton”).

Traditionally preferences were addressed by offering different films andsometimes different photographic papers for different geographicmarkets. Examples are Kodak Professional Portra films and Kodak Ultima100, a professional film marketed in India. With the advent of digitalcapture and digital photofinishing it has become possible to addressthese preferences by customizing a suitable set of image processingparameters.

U.S. Pat. No. 5,300,381, to Keelan et. al., entitled “Customizing aDigital Camera based on Demographic Factors” describes a digital cameracustomized for skin color and redeye based on demographic factors.Regional customization can be implemented at camera manufacturing, aspart of the camera firmware, or by providing different camera menus byregion. Regional optimization of skin tone reproduction is performedusing region-specific matrix coefficients to convert camera RGB valuesto Standard CCIR 709 primaries.

U.S. Published Patent Application 2003/0202194 A1, filed by Torigoe,entitled “Image Processing Apparatus and Information ProcessingApparatus, and Method Therefore”, (hereafter “Torigoe”) addressesgeographic preferences in relation to digital mini labs. Torigoedescribes a color managed photofinishing system with multiple input andoutput devices, referred to as a color conversion apparatus. A storageunit contains output profiles for multiple geographic regions. Twodifferent methods of implementing regional preferences are disclosed. Inthe first case, the operator accesses a user interface, which displays atriangle with 3 different names of regions, for example, America,Europe, and Asia. A preference anywhere inside the triangle can beselected, and the system will generate the appropriate output byblending the stored regional output profiles. The second method ofcustomizing the output is to select preferences for the reproduction ofimportant memory colors, for example, skin, sky, and foliage, andneutral colors. The user interface has a slider that lets the userselect the degree of modification between the standard rendition and thepreferred rendition. Color and tone manipulations include selective huerotations and saturation adjustments of skin tones and brightness andcolor balance adjustments by region. Torigoe focuses on selectivemanipulations of the color and brightness of skin tones without specialconsiderations regarding overall tone reproduction or smoothness of skintone reproduction.

U.S. Pat. No. 6,633,410 B1, to Narushima, entitled “Printer for PrintingVisually Equivalent Images Relative to Displayed Images” (hereafter“Narushima”) addresses geographic preferences in relation tophotofinishing kiosks. Narushima discloses a color-managed printingsystem, which contains a processing section for “desirablereproduction”. This module addresses the observation that the preferredreproduction of common memory colors such as skin, foliage, and blue skymay not be the same as accurate calorimetric reproduction, both in termsof color specification as well as tone scale and image structurecharacteristics. Narushima describes a method for determining thepreferred reproduction of various objects by using a judging method thatmay involve studying the flesh color of a large number of people. Thesepreferences are addressed by selective color manipulations in anapproximately perceptually uniform color space, e.g. CIELAB. Schematicdiagrams of selectively shifting and or contracting colors in CIELAB areshown. The system allows variable selection and processing methods todetermine if a color has to be moved. Such methods may include patternrecognition or analyzing the image to find if data are in apredetermined range. More global manipulations of color are alsopossible. Narushima teaches that the sequence of processing and theimage processing parameters in the desired reproduction section can becustomized for the intended user at the time of shipment.

Patton describes a system where the customer and/or lab can manually orautomatically select the desired skin tone characteristics. Skin tonesare selectively identified in scanned images based on at least onecalorimetric parameter. The skin tones are then automatically modifiedtowards the preferred position, which can be different depending onwhether a dark or a light skin tone was identified. Differentmodifications for dark and light skin tones in a single image arepossible. Skin tone modifications are achieved by color and/or densitybalance shifts, but preferably by employing a 3D LUT, which selectivelymodifies skin tones. While Patton identifies contrast of the face as oneof the parameters that can be customized, the issue of implementing aglobal tone reproduction curve optimized for the rendition of peoplewith a wide range of skin tones is not addressed. Likewise, noconsiderations are given towards obtaining a good texture of skin in thereproduction.

Other inventions use face detection algorithms to treat imagescontaining people differently from scenic pictures without people. Oneexample is given by U.S. Published Patent Application No. US2003/0035578A1, filed by Dupin and Luo, entitled “Method for Processing DigitalImage to Adjust Brightness”, hereafter “Dupin”) which describes a methodfor obtaining improved lightness balance for images containing skin orfaces. The image is initially balanced using known scene balancemethods, followed by an analysis to detect skin colored pixels thatcreates a skin probability map using an adaptive thresholding methodderived from the gradient of the skin probability map. From the detectedskin pixels, a brightness adjustment is calculated from the centerweighted average of the skin colored pixels and predetermined constantsfor typical skin pixel brightness values and general algorithm tuning.Dupin does not teach or offer any direction concerning use or adjustmentof the algorithm for regional or cultural preferences for skinbrightness levels.

The above approaches have the shortcoming of ignoring the importance ofstructure and texture in skin tone reproduction. The relationshipbetween the visually perceived densities of objects in an image scenereproduction compared to those in the original scene is a criticalaspect of image reproduction. Traditionally, conventional silver-halidebased photographic systems have produce a well known non-linear,“S”-shaped relationship between the viewed print density (in the case ofa print system) vs. scene exposure, such as shown by “The Reproductionof Colour” by Dr. R. W. G. Hunt, Fountain Press, England, Fourth ed.,(hereafter “Hunt”), see p. 54. While this type of curve may provide“snappy” reproductions of certain types of scenes, it tends to create aharsh look of peoples faces. With the advent of digital imaging it ispossible to create preferred tonal reproductions from any capturesource, e.g., photographic films, digital cameras, on a large collectionof output media and devices, e.g., photographic, thermal or inkjet paperand any type of electronic display devices, e.g., television, computerdisplays, personal picture viewing devices and electronic paper.

As a general rule, a smooth appearance of skin tones is preferred. Theappropriate texture of skin tones can be achieved using sophisticatedimage processing algorithms, for example, as disclosed in U.S. PublishedPatent Application No. US2003/0223622 A1, filed by Simon et al.,entitled “Method and System for Enhancing Portrait Images”. The approachis complex and processing intensive.

A smooth appearance of skin tones can also be accomplished by muchsimpler means of selecting an appropriate tone reproduction for aparticular situation. U.S. Pat. No. 5,528,339, to Buhr et al., entitled“Color Image Reproduction of Scenes with Color Enhancement andPreferential Tone Mapping”; and U.S. Pat. No. 5,390,036, to Buhr et al.,entitled “Color Image Reproduction of Scenes with Preferential ToneMapping” disclose use of a family of tone reproduction curves optimizedfor skin tone reproduction. In U.S. Pat. No. 5,528,339, viewed densitieson the print were defined as a function of the densities of the originalscene. Limits were provided for the slope of this curve, in particularat medium scene densities, which are representative of skin tones andmid-gray tones. These slope limits are lower than what is currently usedin most color reproduction systems. While such low slopes provide asmooth appearance of skin tones, it has been determined that the image,including the face, often looks too flat, with shadows having a tendencyto look gray and relatively harsh transitions towards highlights.

It is well known to those skilled in the art that the perception ofcolor includes other important attributes in addition to lightness, asaddressed by the tone reproduction curve. Attributes that are frequentlyused in connection with perceptually uniform color spaces are lightness,chroma or saturation, and hue. Preferences for skin tone reproductioncan be expressed in those terms, in particular using the CIELAB system(Yamamoto and K. Töpfer, R. E. Cookingham, “The Quantitative Aspects ofColor Rendering for Memory Colors”, Proceedings of IS&T's 2000 PICSConference, Portland, Oreg., p. 94.). Individual and regionalpreferences for lightness, hue and saturation can be addressed byapplying overall color and density shifts to the image or by selectivelyshifting certain regions of color space, e.g., important memory colors,such as skin tones. This approach is disclosed in Torigoe, Narushima,and EP 1139653 A2, filed by Buhr et al., entitled “Color ImageReproduction of Scenes with Preferential Color Mapping”.

These approaches of selective color manipulations of skin tones ignorethe wider issue of the preferred rendition of people, which alsoincludes hair reproduction and reproduction of whites. Whitereproduction is important for rendering the background of eyes, teethand for retaining good detail in clothing. Moreover, they tend ignorethe importance of a smooth texture and overall appearance of human facesin image reproductions of people.

It would thus be desirable to provide methods and systems, which have animproved smooth rendering of skin tones and an improved rendering ofpeople overall.

SUMMARY OF THE INVENTION

The invention is defined by the claims. The invention, in broaderaspects, provides a method and system for processing a photographicimage, which has lightness values, L*, representing one of thecolorimetric values of an original scene, the photographic image istransformed. The transformed image has a gamma as a function of CIE 1976L*, which includes a dark region having a rising slope, a light regionhaving a falling slope, and a plateau region having a slope constantlywithin 5 percent of a maximum value in said plateau region. The risingslope is at least twice as large as the absolute value of the fallingslope. The plateau region is between 10 L* and 30 L* wide. Gamma is aderivative of visually perceived reproduced CIE 1976 L* versus scene CIE1976 L*. Gamma has a maximum slope between 1.5 and 2.0.

It is an advantageous effect of the invention that improved methods andsystems are provided which have an improved rendering of skin tones andan improved rendering of people overall.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be better understood by reference to the followingdescription of am embodiment of the invention taken in conjunction withthe accompanying figures wherein:

FIG. 1 shows the slope of the tonescale, gamma, as a function of scenelightness (CIE 1976 L*) according to the invention.

FIG. 2 compares the slope of the tonescale, gamma, as a function ofscene L* according to the invention with that of a tonescale fallingoutside the invention.

FIG. 3 shows three tonescales according to the invention with varyingcontrast, reproduced L* displayed as a function of scene L*.

FIG. 4 shows the chroma ratio of skin tones, defined as CIE 1976 a,bchroma, C*, of the reproduction divided by the scene chroma, as afunction of scene L* of the skin tones.

FIG. 5 shows three variations in preferred lightness applied to a singletonescale according to the invention, reproduced L* displayed as afunction of scene L*.

FIG. 6 is a diagrammatical view of an embodiment of the system.

FIG. 7 is a diagrammatical view of another embodiment of the system.

FIG. 8 is a diagram of a test procedure to check if a color reproductionsystem meets the specifications for tonal reproduction according to thisinvention.

FIG. 9 is a diagrammatical view of another embodiment of the system.

FIG. 10 is a diagrammatical view of features of the transform of thesystem of FIG. 9.

FIG. 11 is a diagrammatical view of a user interface of an embodiment ofthe system.

FIG. 12 is a diagrammatical view of additional features of the transformof FIG. 9.

FIG. 13 is a diagrammatical view of another embodiment of the system ofthe invention, in the form of a digital camera.

FIG. 14 is a diagrammatical view of the operation of the camera of FIG.13.

FIG. 15-16 c are diagrammatical views of menus and submenus of thecamera of FIG. 13.

FIG. 17 is a diagrammatical view of another embodiment of the system.

DETAILED DESCRIPTION OF THE INVENTION

The methods and systems disclosed herein relate to a family of tonereproduction curves that produce an improved optimum rendition of peoplein different geographic locations. This family of tonescales is alsoreferred to herein as “geolocalizable tonescales”. The geolocalizabletonescales reduce burnt-out highlights and dark shadows as well as largedifferences in saturation between light and dark skin tones. The maximumslope limits are higher, while still retaining detailed whitereproduction, soft highlights on faces and an overall smooth appearance.The slopes in the scene density region that represents most skin colorsare still lower than for traditional S-shaped slopes of tonescales,leading to lower visibility of noise on faces and an overall smoothtexture of the rendered faces. Higher slopes of the tonescale towardsdarker colors also allow retention of adequate color saturation and gooddetail in black hair.

The geolocalizable tonescales also provide an advantage with respect tothe geolocalized customization of the rendition of people. No selectivemanipulations of specific regions of color space, such as skin toneregions, are required. Geolocalized customization can be achieved bysimple manipulations of color and density balance of the image as awhole. These manipulations are more intuitive to photofinishers and aremore easily maintained by the manufacturer. The approach is particularlypowerful, if a face detection algorithm combined with a density balancealgorithm is run prior to applying the tonescale. The algorithm detectsimages containing people and shifts the density balance of the imageoverall according to a region-specific aim for skin tone reproduction.For example, images containing people can be rendered lighter asreflected by the regional aim, while scenic images are run through astandard color and density balance algorithm that renders them darker toproduce more vivid colors.

In the following description, some embodiments of the present inventionwill be described as software programs. Those skilled in the art willreadily recognize that the equivalent of such software may also beconstructed in hardware. Because image manipulation algorithms andsystems are well known, the present description will be directed inparticular to algorithms and systems forming part of, or cooperatingmore directly with, the method in accordance with the present invention.Other aspects of such algorithms and systems, and hardware and/orsoftware for producing and otherwise processing the image signalsinvolved therewith, not specifically shown or described herein may beselected from such systems, algorithms, components, and elements knownin the art. Given the description as set forth in the followingspecification, all software implementation thereof is conventional andwithin the ordinary skill in such arts.

The computer program may be stored in a computer readable storagemedium, which may comprise, for example; magnetic storage media such asa magnetic disk (such as a hard drive or a floppy disk) or magnetictape; optical storage media such as an optical disc, optical tape, ormachine readable bar code; solid state electronic storage devices suchas random access memory (RAM), or read only memory (ROM); or any otherphysical device or medium employed to store a computer program.

The present invention can be implemented in computer hardware. Referringto FIG. 17, there is illustrated a computer system 110 for implementingthe present invention. Although the computer system 110 is shown for thepurpose of illustrating a preferred embodiment, the present invention isnot limited to the computer system 110 shown, but may be used on anyelectronic processing system such as found in home computers, kiosks,retail or wholesale photofinishing, or any other system for theprocessing of digital images. The computer system 110 includes amicroprocessor-based unit 112 for receiving and processing softwareprograms and for performing other processing functions. A display 114 iselectrically connected to the microprocessor-based unit 112 fordisplaying user-related information associated with the software, e.g.,by means of a graphical user interface. A keyboard 116 is also connectedto the microprocessor based unit 112 for permitting a user to inputinformation to the software. As an alternative to using the keyboard 116for input a mouse 118 may be used for moving a selector 120 on thedisplay 114 and for selecting an item on which the selector 120overlays, as is well known in the art.

A compact disk-read only memory (CD-ROM) 124, which typically includessoftware programs, is inserted into the microprocessor based unit forproviding a means of inputting the software programs and otherinformation to the microprocessor based unit 112. In addition, a floppydisk 126 may also include a software program, and is inserted into themicroprocessor-based unit 112 for inputting the software program. Thecompact disk-read only memory (CD-ROM) 124 or the floppy disk 126 mayalternatively be inserted into externally located disk drive unit 122which is connected to the microprocessor-based unit 112, Still further,the microprocessor-based unit 112 may be programmed, as is well known inthe art, for storing the software program internally. Themicroprocessor-based unit 112 may also have a network connection 127,such as a telephone line, to an external network, such as a local areanetwork or the Internet. A printer 128 may also be connected to themicroprocessor-based unit 112 for printing a hardcopy of the output fromthe computer system 110.

Images may also be displayed on the display 114 via a personal computercard (PC card) 130, such as, as it was formerly known, a PCMCIA card(based on the specifications of the Personal Computer Memory CardInternational Association), which contains digitized imageselectronically embodied in the card 130. The PC card 130 is ultimatelyinserted into the microprocessor based unit 112 for permitting visualdisplay of the image on the display 114. Alternatively, the PC card 130can be inserted into an externally located PC card reader 132 connectedto the microprocessor-based unit 112. Images may also be input via thecompact disk 124, the floppy disk 126, or the network connection 127.Any images stored in the PC card 130, the floppy disk 126 or the compactdisk 124, or input through the network connection 127, may have beenobtained from a variety of sources, such as a digital camera (not shown)or a scanner (not shown). Images may also be input directly from adigital camera 134 via a camera docking port 136 connected to themicroprocessor-based unit 112 or directly from the digital camera 134via a cable connection 138 to the microprocessor-based unit 112 or via awireless connection 140 to the microprocessor-based unit 112.

The output device provides a final image that has been subject to thetransformations. The output device can be a printer or other outputdevice that provides a paper or other hard copy final image. The outputdevice can also be an output device that provides the final image as adigital file. The output device can also include combinations of output,such as a printed image and a digital file on a memory unit, such as aCD or DVD.

The present invention can be used with multiple capture devices thatproduce digital images. For example, FIG. 17 can represent a digitalphotofinishing system where the image-capture device is a conventionalphotographic film camera for capturing a scene on color negative orreversal film, and a film scanner device for scanning the developedimage on the film and producing a digital image. The capture device canalso be an electronic capture unit (not shown) having an electronicimager, such as a charge-coupled device or CMOS imager. The electroniccapture unit can have an analog-to-digital converter/amplifier thatreceives the signal from the electronic imager, amplifies and convertsthe signal to digital form, and transmits the image signal to themicroprocessor-based unit 112.

The microprocessor-based unit 112 provides the means for processing thedigital images to produce pleasing looking images on the intended outputdevice or media. The present invention can be used with a variety ofoutput devices that can include, but are not limited to, a digitalphotographic printer and soft copy display. The microprocessor-basedunit 112 can be used to process digital images to make adjustments foroverall brightness, tone scale, image structure, etc. of digital imagesin a manner such that a pleasing looking image is produced by an imageoutput device. Those skilled in the art will recognize that the presentinvention is not limited to just these mentioned image processingfunctions.

The general control computer shown in FIG. 17 can store the presentinvention as a computer program product having a program stored in acomputer readable storage medium, which may include, for example:magnetic storage media such as a magnetic disk (such as a floppy disk)or magnetic tape; optical storage media such as an optical disc, opticaltape, or machine readable bar code; solid state electronic storagedevices such as random access memory (RAM), or read only memory (ROM).The associated computer program implementation of the present inventionmay also be stored on any other physical device or medium employed tostore a computer program indicated by offline memory device. Beforedescribing the present invention, it facilitates understanding to notethat the present invention is preferably utilized on any well-knowncomputer system, such as a personal computer.

It should also be noted that the present invention can be implemented ina combination of software and/or hardware and is not limited to devices,which are physically connected and/or located within the same physicallocation. One or more of the devices illustrated in FIG. 17 may belocated remotely and can be connected via a network. One or more of thedevices can be connected wirelessly, such as by a radio-frequency link,either directly or via a network.

The present invention may be employed in a variety of user contexts andenvironments. Exemplary contexts and environments include, withoutlimitation, wholesale digital photofinishing (which involves exemplaryprocess steps or stages such as film in, digital processing, printsout), retail digital photofinishing (film in, digital processing, printsout), home printing (home scanned film or digital images, digitalprocessing, prints out), desktop software (software that appliesalgorithms to digital prints to make them better—or even just to changethem), digital fulfillment (digital images in—from media or over theweb, digital processing, with images out—in digital form on media,digital form over the web, or printed on hard-copy prints), kiosks(digital or scanned input, digital processing, digital or hard copyoutput), mobile devices (e.g., PDA or cell phone that can be used as aprocessing unit, a display unit, or a unit to give processinginstructions), and as a service offered via the World Wide Web.

In each case, the invention may stand alone or may be a component of alarger system solution. Furthermore, human interfaces, e.g., thescanning or input, the digital processing, the display to a user (ifneeded), the input of user requests or processing instructions (ifneeded), the output, can each be on the same or different devices andphysical locations, and communication between the devices and locationscan be via public or private network connections, or media basedcommunication. Where consistent with the foregoing disclosure of thepresent invention, the method of the invention can be fully automatic,may have user input (be fully or partially manual), may have user oroperator review to accept/reject the result, or may be assisted bymetadata (metadata that may be user supplied, supplied by a measuringdevice (e.g. in a camera), or determined by an algorithm). Moreover, thealgorithm(s) may interface with a variety of workflow user interfaceschemes.

The invention is inclusive of combinations of the embodiments describedherein. References to “a particular embodiment” and the like refer tofeatures that are present in at least one embodiment of the invention.Separate references to “an embodiment” or “particular embodiments” orthe like do not necessarily refer to the same embodiment or embodiments;however, such embodiments are not mutually exclusive, unless soindicated or as are readily apparent to one of skill in the art.

In the following, relationships are described between scene colorimetryand colorimetry of the reproduced image that produces final images.Those relationships can be equally described in terms of colorimetry orvisually perceived densities of objects in a scene reproduction comparedto those in the original scene. Scene colorimetry is defined as the CIEtristimulus values, XYZ, of colored objects in a scene under a givenilluminant, calculated according to the color-matching functions of theCIE 1931 Standard Colorimetric Observer Colorimetry of the reproducedimage refers to the CIE tristimulus values, XYZ, of the reproducedobjects, in hardcopy or softcopy, under a given illuminant calculatedaccording to the color-matching functions of the CIE 1931 StandardColorimetric Observer. In the discussion herein, the scene andreproduction illuminants are chosen as the CIE Standard Illuminant D50.This is not limiting. The encoding of scene and reproductioncolorimetry, i.e. the numerical specification of color information, isnot limited to CIE XYZ values. Any reversible transformation between CIEXYZ values of real surface colors and other color encoding metrics canbe used, e.g. CIELAB, CIELUV, tristimulus values of any linearcombination of the color-matching functions of the CIE 1931 StandardColorimetric Observer, nonlinear encoding metrics of tristimulus values.In the discussion herein, scene and reproduced colorimetry arerepresented in terms of CIE 1976 CIELAB values. This selection alsodefines the measurement methods of color and the signal-processingtransformations that determine the meaning of encoded color values. Thisis not limiting. It is well known in the art that viewing conditionsmust be defined in addition to colorimetry in order to fully defineappearance of color and tone in original scenes and images. It iscustomary to assume a set of reference viewing conditions in the designof color and tone reproduction systems. Such conditions may includeviewing flare, the type of viewing surround, the average luminance andthe adaptive white point, and are well known to those of skill in theart, for example, those associated with the definition of ICC ProfileConnection Space (PCS, Specification ICC.1:2003-09, File Format forColor Profiles (Version 4.1.0)) for viewing hardcopy and softcopy imagereproductions ((E. J. Giorgianni, T. E. Madden, “Digital ColorManagement”, Addison-Wesley, 1997, p. 528). Average viewing conditionsassumed for scene capture are also given by Giorgianni and Madden (p.503).

As discussed above, tone reproduction can be defined in an equivalentfashion as the relationship between the visual densities of thereproduction and the visual densities of the original scene. A metricthat can be interchangeably used with CIE 1976 L* values is the visualdensity of the original scene or the reproduction. Visual density,D_(v), can be calculated from the Y component of the CIE XYZ values forCIE Standard Illuminant D50 using the following equation:

D _(v)=−log 10(Y/100)  (1).

FIG. 1 shows the slope of a tone reproduction curve (also referred toherein as “gamma”) that is the derivative of reproduced CIE 1976lightness, L*, versus scene CIE 1976 L*. FIG. 1 shows that this slope isrising steeply from dark colors towards a constant value at mid tones,and is then decreasing more slowly towards whites. Most natural skintones have scene lightness values between 30 and 80. This asymmetry inthe slope profile guarantees that transitions between dark and lightskin tones are soft, and so are highlights on faces. On the other handthis type of tone reproduction retains plenty of detail in black hairdue to the steeper slope towards dark colors.

The asymmetry requirement can be defined by looking at the secondderivative of the tone reproduction curve, which can be estimated overspecific regions as follows. In the dark region, an estimate of thesecond derivative can be obtained by subtracting the gamma values,γ_(L2) and γ_(L1), at scene L* values of 20 and 10 (parts 12 and 10 inFIG. 1) and by dividing by the L* difference of 10 according to Eq. 2a:

$\begin{matrix}{s_{1} = {\frac{\gamma_{L\; 2} - \gamma_{L\; 1}}{10}.}} & ( {2a} )\end{matrix}$

An estimate of the slope in the light region can be likewise calculatedby subtracting the gamma values, γ_(L8) and γ_(L5), at scene L* valuesof 80 and 50 (parts 16 and 14 in FIG. 1) and by dividing by the L*difference of 30 according to Eq. 2b:

$\begin{matrix}{s_{2} = {\frac{\gamma_{L\; 8} - \gamma_{L\; 5}}{30}.}} & ( {2b} )\end{matrix}$

It has been determined that pleasing, smooth reproduction of skin tonescan be obtained, if gamma as a function of scene L* meets the followingcriteria:

-   -   (a) The rising slope in the dark region, s₁, is at least twice        as big as the absolute value of the falling slope in the light        region, s₂, as expressed in Eq. 3:

s ₁≧2·|s ₂|  (3).

-   -   (b) The plateau region of nearly constant slope (18 in FIG. 1)        is at least 10 L* wide, but no wider than 30 L* units. Nearly        constant slope means that gamma is within 5% of its maximum        value.    -   (c) The maximum slope, gamma, is between 1.5 and 2.

FIG. 2 shows the slope of the tone reproduction curve, gamma, as afunction of scene L* for a geolocalizable tonescale (designated byreference number 20) compared with a tonescale (designated by referencenumber 22) that exhibits S-shape characteristics and falls outside theinvention. It can be clearly seen that, in the latter case, the maximumslope falls outside the range specified above, and that the twoderivatives s₁ and s₂ are very similar in magnitude. FIG. 3 shows acontrast series of curves, displayed as reproduced L* as a function ofscene L* of a geolocalizable tonescale.

Another important aspect of producing a smooth appearance and a pleasingtexture of faces is the change in color saturation or chroma as afunction of the lightness (CIE 1976 L*) of skin tones. TraditionalS-shaped tone reproduction curves tend to reduce the chroma of lightcolors in the reproduction while enhancing darker skin tones, oftengiving them a saturated orange appearance, which is not preferred byviewers. Requirements for smooth chroma reproduction are most easilyquantified if the chroma ratio of reproduced skin colors (CIE 1976 a,bchroma, C*) is divided by the corresponding C* values in the originalscene. This chroma ratio is displayed in FIG. 4 as a function of L* ofthe skin tones in the original scene. Preferred reproductions of peopleare obtained if the slope of the curve shown in FIG. 4 meets certainrequirements:

-   -   (a) The difference of the chroma ratios at scene L* values of 75        and 50 (parts 26 and 24, CR₇₅ CR₅₀) divided by the L* difference        of 25 must fall below the threshold of 0.04 given in Eq. 4:

$\begin{matrix}{s_{3} = {{\frac{{CR}_{75} - \gamma_{50}}{25}} \leq {0.04.}}} & (4)\end{matrix}$

-   -   (b) The slope of the curve between L* values of 25 and 50 must        be smaller or equal to s₃ defined in Eq. 4, but not negative.    -   (c) The chroma ratio for skin tones at a mid tone scene L* value        of 60, part 28, must fall between 0.75 and 1.25.        It preferred that the geolocalizable tonescales meet these        criteria.

As is known in the art, individual and regional preferences forlightness, hue and saturation can be addressed by applying overall colorand density shifts to the image or by selectively shifting certainregions of color space, e.g., important memory colors, such as skintones. The term individual preference refers to the preferred skin tonereproduction of an individual lab or person. Regional preference refersto the average preferred skin tone reproduction in a given country orregion.

It has been determined that color and density shifts applied to thewhole image are effective in producing pleasing skin tones and overallreproductions of the images, if the tone reproduction curves accordingto the invention are used. The geolocalizable tonescales also minimizedeleterious effects on the reproduction of other colors in the image,e.g., other memory colors, foliage, blue sky, near neutral colorsincluding blacks and whites, colorful fabrics, flowers. The relationshipof skin tones to overall reproduction of an image is often referred toas skin-to-neutral reproduction. It has been determined that there islittle benefit in applying shifts to selected regions of color space, ifthe neutral reproduction that corresponds to the preferred skin tonereproduction meets the following criteria:

-   -   (a) The reproduced CIELAB a* and b* values of the 20% gray        corresponding to the preferred skin tone reproduction fall into        the ranges of −3<a*<3 and −10<b*<2.    -   (b) The reproduced CIELAB a* and b* values of the 75% reflector        (Munsell N9 according to the Munsell Book of Color)        corresponding to the preferred skin tone reproduction fall into        the ranges of −1<a*<3 and −5<b*<0.    -   (c) The reproduced CIELAB a* and b* values of a 2.5% reflector        (e.g. black cloth) corresponding to the preferred skin tone        reproduction fall into the ranges of −1<a*<3 and −6<b*<0.    -   (d) The L* shifts required for preferred skin tone reproduction        compared with the preferred reproduction of other colors do not        exceed an absolute value of 12.        It is believed that few regional and individual preferences for        skin tone reproduction would fall outside these ranges. The L*        shifts of part (d) for skin tones and non-skin tones can be        readily predetermined empirically. Digital images can be readily        tested for these criteria to determine whether the        geolocalizable tonescales would be likely to provide a suitable        result.

FIG. 5 shows a tone reproduction curve according to the currentinvention with three different adjustments for preferred skin tonelightness.

The tone reproduction curves according to the invention in combinationwith customized setups to meet regional preferences for skin tonereproduction can be implemented in a wide variety of color reproductionsystems, intended to provide hardcopy or softcopy reproductions oforiginal scenes. Some examples are given below.

Capturing the original scene parameters can be accomplished by any lightsensitive element, or sensor, capable of sensing the tonal values of theobjects in a scene in a manner, which quantitatively determines theirrelative log luminances. The sensor is typically contained in a deviceor camera, which controls its exposure to light. Examples of cameras andsensors include but are not limited to cameras using photographic filmsand electronic cameras using CCD (Charge-Coupled Device) sensors.Cameras and sensors may be of any suitable physical dimensions.

FIG. 6 shows an embodiment of the system. The sensors in conventionalphotographic applications are silver halide based photographic materialsthat may be negative or positive working film, semi-reflective film, orreflection paper although the most common embodiment is color negativefilm. Conventional films and papers contain a multilayer structure withseparate color record imaging materials. Films specifically designed forscanning are also appropriate. The film may or may not be contained inspools, cartridges, or similar containers, depending on the type ofcamera in which it is used. The film may contain non-optically sensitivematerials, such as magnetic or electrical elements. Scene capture may beaccomplished using all currently available silver halide photo-sensitivefilms and papers as well as those that will appear in the future.

In silver halide photography, the scene is captured and stored as latentimage in the silver halide emulsion grains. Subsequent to or concertedwith photosensitive element exposure, the recorded information is oftenconverted to a more permanent representation of the original sceneparameters by some process, typically chemical although it can be alsobe thermal, magnetic, optical, or electrical in nature. The resultantrecorded image is typically a transparent film, although it may be areflection material or any other storage medium. A typical embodimentfor conventional silver halide photography is the use of a 35 mm singlelens reflex camera exposing color negative film 30 followed by Kodak™Flexicolor™ C-41 chemical development 32 (marketed by Eastman KodakCompany of Rochester, N.Y.) to produce an optical density varyingrepresentation of the original scene.

The visual reproduction of the original scene in the form of a hardcopyprint 36 can be generated by optically printing a photographic film 30onto silver halide photographic or other light sensitive paper 36. Theprinting process can be additive or subtractive and the photographicmaterials can be negative or positive working (negative film withnegative paper or positive film with positive paper). To achieve thepreferred final viewed reproduction, the paper response characteristicsmust be accounted for in the film to be printed so that the resultantproduced image has the desired tone reproduction characteristics. Asuitable embodiment of the optical printing process is an optical minilab 34.

Steps 30 and 32 are also appropriate as input for digitalphotofinishing, but films and/or development processes not suitable forconventional optical printing may be used. A film intended for scanningcan be characterized by having low suitability for both direct viewing(e.g., projection) and optical printing. The film intended for scanningmay be suitable for wet, aqueous processing including lamination andchemical transfer methods, or it may be suitable for dry, thermalprocessing by being comprised of incorporated development chemicals.Apparently dry photo processes in conjunction with conventional silverhalide films may also be used, such as in the Film Processing Station(FPS) offered Kodak Picture Maker G3 kiosk. When the film is insertedinto the FPS, a proprietary developing agent is applied to the film withno resulting by-product, and the film is directly scanned. The widerrange of suitable films and chemical processes for development isindicated by element 34. The processed film is scanned, digitallyprocessed and printed in a digital mini lab, an example of which isdescribed in greater detail by U.S. Pat. No. 6,574,373 B1, to Morba andHicks, entitled “Method and Apparatus for Printing Digital Images”. Theimages may be printed on silver halide paper or any other suitablereflective print media 42. Many non-light-sensitive imaging materialsare conveniently used by electronic printing processes to producehigh-quality reproductions. The printing process can be based on manytechnologies. The method of image formation can be half-tone, continuoustone, or complete material transfer. The imaging material can betransparent film, reflective paper, or semi-transparent film. Thematerials can be written on to produce pictorial images by thermal dyetransfer, ink jet wax, electrophotographic, or other pixelwise writingtechniques. These processes use three or more colorants to createcolored pictorial representations of pictorial scenes. The colorants maybe dyes, toner, inks, or any other permanent or semi-permanent coloredmaterial. Many non-light-sensitive imaging materials are convenientlyused by electronic printing processes to produce high-qualityreproductions. The printing process can be based on many differenttechnologies. The method of image formation can be half-tone, continuoustone, or complete material transfer. The imaging material can betransparent film, reflective paper, or semi-transparent film. Thematerials can be written on to produce pictorial images by thermal dyetransfer, ink jet, wax, electrophotographic, or other pixelwise writingtechniques. These processes use three or more colorants to createcolored pictorial representations of pictorial scenes. The colorants maybe dyes, toner, inks, or any other permanent or semi-permanent coloredmaterial.

A digital representation of the images may also be written to permanentstorage media, e.g., floppy disks, Picture CDs or DVDs 44. The imagesstored in such form may be read into a personal computer 46 anddisplayed by on the computer monitor 48 by suitable softwareapplications. Assuming the personal computer is connected to a networkthe images may also be submitted to an online print service 50 to obtainhardcopy prints. Alternatively, the digital storage media can be used inportable electronic picture display 47 with a preferred display size ofat least 4×6 inches. Suitable display technologies include by are notlimited to CRT (cathode ray tube), LCD (liquid crystal display), OLED(Organic Light Emitting Diode) and plasma displays. An example of such aviewing device is the Epson P-1000 PhotoViewer, which uses LCDtechnology, although the image diagonal of 3.8″ of this device issmaller than desired.

The invention describes the tonal relationship between the visuallyperceived densities of objects in the image scene reproduction, asexemplified by 36, 42, 47, 48 and 50 in FIG. 6, compared to those in theoriginal scene. While those skilled in the art will recognize that thetonal properties of the reproduction in sequences 30, 32, 34, 36, andalternatively 30, 38, 40, 42 can be tightly controlled, the alternativeoutput paths rely on a file format on the storage medium 44 that can becorrectly interpreted by subsequent applications in order to produce theintended tonal reproduction. A form of color encoding commonly used atthe present time is sRGB (IEC 61966-2-1) in combination with the ICCcolor management paradigm. It is also assumed that the output devicesand media 47, 48, 50 are calibrated to reproduce colors encoded in ICCprofile connection space (PCS). FIG. 8 describes a test procedure tocheck if a color reproduction system meets the specifications for tonalreproduction according to this invention.

FIG. 7 shows a diagram of another embodiment of the system used fordigital scene capture. The image sensors in digital cameras 52 can be,but are not limited to single-chip color charge-coupled devices (CCD) orCMOS image sensors. The analog output signal from the image sensor isconverted to digital data by an analog-to-digital (A/D) converter. Thedigital data is processed by a CPU or digital signal processor. Theprocessed digital image file is provided to a memory card interface,which stores the digital image file on the removable memory card 54 oron another type of digital memory device, such as a floppy disk ormagnetic hard drive. The removable memory card 50, which is well-knownto those skilled in the art, can include, for example, a memory cardadapted to the PCMCIA card interface standard, as described in the PCCard Standard, Release 2.0, published by the Personal Computer MemoryCard international Association, Sunnyvale, Calif., September 1991. Theremovable memory card 30 can also be adapted to the Compact Flashinterface standard, such as described in the CompactFlash SpecificationVersion 1.3, published by the CompactFlash Association, Palo Alto,Calif., Aug. 5, 1998, or to other memory devices such as the well-knownSSFDC (Solid State Floppy Disc Card) and Memory Stick formats orSmartMedia™ cards.

The camera 52 or the storage medium can be directly connected to apersonal printer 58 such as the Kodak Printer Dock 6000 marketed byEastman Kodak Company, which produces hardcopy prints using thermalprinting technology. Suitable output technologies were discussed inconnection with part 42 in FIG. 6. Alternatively, the removable memorycard 54 may be read by the input unit of a digital mini lab 62 or akiosk 64. Units 62 and 64 are both capable of producing hardcopy printson reflective media 66 and of writing digital representations of theimages to permanent storage media. This section is identical to theoutput of the mini lab 40 discussed in FIG. 6. The operation of animaging kiosk, such as a Picture Maker® kiosk produced by Eastman KodakCompany, is describe in U.S. Published Patent Application No. U.S.2004/0041819 A1, filed by Barry and Minns, entitled “System and Methodfor Generating an Image Fulfillment Order”. Alternatively, the removablememory card can be used in portable electronic picture display 56analogous to 47 in FIG. 6. Moreover, the removable memory card may beread by a personal computer 70 using a special card reader as aperipheral or by directly connecting the camera to the computer, whichcommonly done using the Universal Serial Bus (USB) interface.

As discussed in connection with FIG. 6, the images may be displayed byon the computer monitor 48 by suitable software applications. The imagesmay also be printed by a personal printer 72 to generate a hardcopy onsuitable reflective print media 60. Printers 58 and 72 may be the samedevice, or they may be different and use different printingtechnologies. Assuming the personal computer is connected to a networkthe images may also be submitted to an online print service 76 to obtainhardcopy prints.

The methods and systems herein relate to the tonal relationship betweenthe visually perceived densities of objects in the image scenereproduction, as exemplified by 56, 60, 66, 74 and 76 in FIG. 6,compared to those in the original scene. In this case, the file formatand the color encoding on the storage medium 54 that must be universallyunderstood and correctly interpreted by subsequent applications in orderto produce the intended tonal reproduction.

A form of color encoding commonly used at the present time is sRGB (IEC61966-2-1) in combination with the ICC color management paradigm. It isassumed that the output devices and media 56, 58/60, 66, 74, 76 arecalibrated to reproduce colors encoded in ICC profile connection space.

FIG. 8 illustrates a test procedure to check if a color reproductionsystem meets the specifications for tonal reproduction according to thisinvention. This procedure can be used as an initial test and on anongoing basis to determine if a particular system remains within thespecification. In this test procedure, two test targets 80, 82 ofuniform size are provided. Target 80 is a spectrally uniform gray, i.e.it exhibits constant percent reflectance (20%) in a wavelength spectrumof from 380 nm to 780 nm. Target 82 is a target with multiple neutraland skin tone patches covering the full range of potential visualdensities of these objects in the scene. An example of a suitable targetis the GretagMacbeth Digital Color Checker SG. Both targets are largeenough so that when photographed as described below, each targetsubstantially fills the image capture area of the capture device.

A lighting system 84 is provided to uniformly illuminate the targets,mounted on a uniform gray (20% reflectance) background, at approximatelya 45° angle of incidence. The lighting should provide reasonablyspecular illumination typical of high quality, low flare viewingconditions. The spectral quality of the lighting should be similar tothat for which the imaging system under test is designed. Under constantillumination conditions from lighting system 84 and with a scene captureapparatus 86, e.g. a photographic or digital camera, orientedperpendicularly to the targets, each of the target images is capturedaccording to ISO standards for the image capture device. Additionally,the reflection spectra of each color patch in target 82 and thecorresponding area of target 82 are measured using a very low flaretelespectroradiometer 94. A suitable embodiment is the Photo Researchtelespectroradiometer 705. Each measurement is made with a spot sizeone-fourth as large as the density step area being measured. Usingidentical lighting, image device and radiometer conditions, target 80 iscaptured and measured as described above.

Using the imaging system 88 under analysis including scene captureapparatus 86 and image reproduction stage 90 and having an overalltransformation characteristic represented by transformation box 92, ahardcopy reproduction of the target images is produced by a suitableoutput device. The reproduction is made in such a manner that the N/3.5Grey patch in the reproduction match those of the original Munsell N/3.5Grey Patch. A 1.0 scene density relative to a 100% diffuse reflector isreproduced at a density of 1.0+0.05.

The reproduced prints are uniformly illuminated with lighting system 84at a 45° angle of incidence and the visual step densities are measuredwith the very low flare radiometer 94. It will be understood that thetargets and reproductions preferably are illuminated and measured underidentical conditions. These measurements include the target andreproduction illuminant. If this is not the desired capture and viewingilluminant, the illuminant spectrum can be divided out, if the spectralreflectance of one of the neutral target patches in target 82 is known.CIE XYZ values for all patches are calculated from the target andreproduction reflectance spectra, the spectrum of the illuminant, andthe CIE color-matching functions of the observer, using standardmethods. Before proceeding, the measured XYZ values on the target 82have to be corrected for any target illumination non-uniformity usingthe target 80 measurements in the same location as the target 82 stepsLikewise, the measured step XYZ values on target 96, the reproduction oftarget 82, must be corrected for any target illumination non-uniformity,any field exposure non-uniformity by the scene capture apparatus 86 ontothe film or sensor and any field exposure non-uniformities present inthe hardcopy image reproduction apparatus 90 using target 98. CIELABvalues for the target and the reproduction, referring to the CIEStandard Illuminant D50, are calculated using standard procedures.

The reproduction of the targets on softcopy devices can be measuredusing the same telespectroradiometer. Since these devices areself-luminous displays, the target illumination system 84 is not needed.The measurements are performed in the absence of any ambientillumination.

If the sophisticated lighting setup and measurement equipment describedabove is not available it may also be possible to directly measurevisual densities of the original chart and the hardcopy reproductionusing a suitable reflection densitometer, such as an X-Rite 310. In thiscase, however, it would not be possible to test the requirements forchroma reproduction of skin tones and for deviations from neutral andviewing flare according to the assumed standard viewing conditions mustbe added. Smaller clip-on colorimeters, such as the MonacoOPTIXXR, canalso be used to characterize softcopy displays.

EXAMPLE 1

In a particular embodiment, exposed Kodak Gold 200 Gen. 6 film isprocessed by Kodak™ Flexicolor™ C-41 chemical development and submittedto a digital mini lab for printing. Kodak Gold 200 film was used as arepresentative example of color negative films from a variety ofvendors.

The processed roll of film was submitted to a digital mini lab forprinting. Referring to FIG. 9, the digital mini lab 100 includes ascanner 104, which is designed to receive and scan a roll of developedfilm 102. The roll of developed film 102 is transported past a sensor inscanner 104, which scans the images on the film 102 so as to provide adigital record of the customer images. The scanner 104 scans at aresolution sufficient to provide the desired quality prints, preferably,at a resolution of at least 1000×1500 pixels per inch for a 35 mm filmframe, and more preferably at a high resolution equal to or greater thanabout 2000×3000 pixels per inch for the 35 mm film frame. Examples ofsuitable scanners include the Pakon F-235 scanner, the Kodak HR-200, andHR-500 scanners, the Kodak 1640 and 1650 scanner, Noritsu scannerssupplied with Noritsu digital mini labs such as the QSS3011 and otherQSS3XXX series mini labs.

The digital record of the image is forwarded to an image data manager(IDM) 106 wherein the images are manipulated as preprogrammed. In theembodiment illustrated, IDM 106 comprises a computer (microprocessor110) used for manipulation of the digital images contained in thedigital record file. The IDM 106 includes a memory 108 for storing ofthe digital record of the customer image order.

The IDM 106 contains an electronic printing device 118, which exposesthe individual images of the customer order onto photosensitive material120. Devices which can be used to print on light-sensitive materialsinclude CRT, LED (Light Emitting Diode), LVT (Light Valve Technology),LCD, Laser, as well as any other controlled optical light generatingdevice. All these devices have the ability to expose 3 or morelight-sensitive layers in a light-sensitive material to produce acolored image. They differ mainly in the technology on which the devicesare based. In the particular embodiment illustrated, the digital printer118 is a MLVA (Micro Light Valve Array) printer with a resolution of 400ppi printer or a laser printer with a resolution of at least 300 ppi.The printer scans a light containing image data onto cut sheets as theymove past an exposure gate. In order to produce smooth, high qualityreproductions of people the printer must have at least a resolution of250 dpi (dots per inch) and 8 bits of information per color channel. Anexample of such a image printer device would be a Noritsu QSS3011 minilab system with a scanner capable of resolution in excess of 2000 pixelsper inch and a laser printer with a resolution of 320 pixels per inch.The photosensitive material 120 is KODAK EDGE Generations Paper.

A CPU (computer) 110 is provided for controlling operation of theapparatus and its various components. A user/operator interface 112,which includes a viewing screen 114, is also provided, for allowing anoperator to enter instructions for operation of the apparatus andmonitor operation of the apparatus as is customarily done. Any regionalcustomization of the image processing can be entered via this interface.

An appropriate computer printing program is provided for controllingoperation of the IDM 106. The computer program is provided in anappropriate format which allows loading of the program into theapparatus 100 which causes the IDM 106 to perform the required steps. Inparticular, the computer program is designed so that the IDM 106 willfirst obtain and store a complete customer image order prior toprinting. Appropriate enhancement algorithms, which have beenpreprogrammed into IDM 106, are applied to the customer image order soas to improve the overall aesthetic appearance of the images whenprinted. It is to be understood that any desired enhancements and/orcorrections may be applied to the images. For example, but not by way oflimitation, the following are a few of the enhancements that may beapplied: contrast adjustment, red eye removal, color balance, removal ofdust marks or scratches and sharpness adjustments. In addition, customcorrections, such as crop and zoom, can be programmed or manuallyentered into the digital printer. The implementation of the tonescaleaccording to the invention is part of this image processing sequence.After the stored digital images are enhanced, they are forwarded to theprinter 118 for printing.

FIG. 10 shows the sequence of image processing steps that is required inorder to implement the geolocalized tonescale according to the inventionin combination with regional settings for the preferred reproduction ofpeople. After scanning the film 102 with scanner 104 a digitalrepresentation of the images is stored in the memory 108 of the IDM 106.These scanner code values 122 preferably represent film densities. Forany further processing it is advantageous transform the scanner codevalues 122 to a common printing density space 124. The calculation ofscanner and printing densities is well known in the art and is describedby Giorgianni and Madden, p. 456, 457. The term printing densitytraditionally referred to the densities of the film as “seen” by thephotographic paper in an optical printer with a particular light source.The film transmittance corresponding to density is calculated as thenormalized integral of the product of the film spectral transmittancewith the filtered spectral distribution light source (and lens) of theprinter and the spectral sensitivity of the receiving medium, in thiscase photographic paper.

It is possible to produce scanners with spectral responsivities thatapproximate the case of optical printing. This match is never perfectand individual scanners may vary. Therefore it is advantageous toconvert the actual scanner densities to reference scanner densities fora common well-defined scanner, which closely resemble optical printingdensities. This can frequently be accomplished by transforming theoriginal scanner densities 122 with a LUT and matrix to producereference scanner densities 124. For the convenience of using 12 bitintegers in image processing and storage the original densities aremultiplied by a factor of 1000.

The best renditions of people are obtained the reproduced images containno visible image structure artifacts, e.g., noise. Therefore it isadvantageous but not required to apply a noise reduction algorithm. Anexample of a suitable algorithm is disclosed in European PatentPublication No. EP1093088 B1, filed by Gindele, entitled “A regiongrowing based noise reduction method for digital images”. This algorithmuses a sparse local neighborhood in form of a snowflake in order toapply noise reduction only to regions that do not contain edges, thussufficiently reducing noise while retaining good edge sharpness. Noisereduction algorithms work based on thresholds and they normally need anestimate of the image noise as a function of digital code values. Thoseskilled in the art will recognize that such tables may be generated inadvance by characterizing the noise of a certain film/scannercombination. Noise tables may also be generated by automatic noiseestimation using the actual images of a photofinishing order, asdisclosed by European Patent Publication No. EP1205878 A2, filed byGindele and Serrano, entitled “Estimating noise for a digital imageutilizing updated statistics”.

As a next step, a scene balance algorithm 130 is applied in order to mapa predetermined visual scene density to a predetermined digital codevalue. The algorithms are commonly known as “white-balance,”“color-constancy” or “scene-balance” algorithms. These algorithms canwork on a single image, several images, or an entire set of images. Anexample of a suitable scene balance algorithm is described by E. Goll etal., “Modern Exposure Determination for Customizing PhotofinishingPrinter Response”, Journal of Applied Photographic Engineering, 2, 93(1979). Further improvements in scene-balance algorithms might includemixed illuminant detection and subject detection.

For a perfect neutral balance, for example, the 20% reflector may bemapped to a code value of 1644. However, it is understood by thoseskilled in the art that all scene balance algorithms have somedistribution of errors and that the above requirement is never perfectlymet. Averaged over a large number of scenes the algorithm is able tomeet the above aim. It may be the case that the above specificationproduces on average good skin tone renditions in one geographic region,but that a different skin tone rendition is preferred in anothergeographic region. The appropriate color and density balance offset toproduce good skin tone renditions in the second region may be suppliedto the scene balance algorithm 130 via the regional parameter set 1(reference number 132), so that the balance of the overall population ofimages is shifted by the specified amount.

The aims for such manipulations based on the optimum skin tonereproduction for a given geographic regions can be obtained incontrolled psychophysical studies of color and tone attributes such asthose described in Chapter 20 of the Handbook of Image Quality (B. W.Keelan, “Handbook of Inage Quality”, Marcel Dekker, 2002).

It is often the case that the preferred color and density balance ofscenes containing people is different from scenic images without people.For example, a lighter balance may be preferred for scenes containingpeople, but this may make scenic images appear too washed out. This canbe addressed by including a skin detection algorithm 134 in the imageprocessing sequence in order to apply different balances to both typesof scenes. A suitable algorithm is disclosed in U.S. Published PatentApplication No. US2003/0035578 A1, which is hereby incorporated byreference. This algorithm uses an aim density for the preferredrendition of skin tones, which again may be customized by geographicregion. The regional parameter 2 (reference number 138) determines themagnitude of the brightness adjustment performed by the algorithm 136.As an alternative, this and like parameters can be set manually by anoperator based upon trial and error.

The image processing sequence may optionally include a scene-dependenttone enhancement algorithm, which enhances highlight and shadow detailof scenes with dynamic range (exposure ratio of the lightest and darkestparts of the original scene) too large to be accommodated by the outputmedium 144. Suitable algorithms are disclosed in U.S. Pat. No. 6,594,388B1, to Gindele et al., entitled “Color image reproduction of scenes withpreferential color mapping and scene-dependent tone scaling”. Thesealgorithms, specifically those that analyze and modify the tone scaleand noise levels in the image, may be configured for optimal regionalskin reproduction performance with the tone reproduction curvesdescribed in this invention. The configuration of these algorithms couldbe set as defaults on system start-up or could be modified by theoperator from the appropriate user interface screens as overalldefaults, or on an order-by-order or image-by-image basis selectedduring preview and editing operations. Finally the rendering transformmaps the digital representation of the scene enhanced by modules 128,130, 136, 140 to code values, which are suitable for the output module.

The regional customization parameters 132 and 138 may be preloaded froma database for a given geographic region or country before the apparatusis shipped to the customer. The customer may fine tune this setting froma user interface 112 of the digital mini lab 100.

An example of a suitable user interface is shown in FIG. 11. Theinterface includes verbal descriptions 150 of the categories that can bemodified, e.g., country, color balance. Any text in FIG. 11 may bedisplayed in different languages. Optionally the display screen mayinclude one or more reference images 164 that show the user the effectof the changes in real time. The user can select from a number ofavailable countries and regions using the menu 152. This loads therecommended settings for color and density balance and skin preference,showing the corresponding positions of the sliders 154 relative toscales 156 and shifts in numeric form 158. The user may then eitherenter new numerical values 158 or move the sliders 154 to change thepreferred shifts. The user may save the new settings using radio button162 or return to the previous settings by pressing the “Cancel” button160. The new settings are communicated to the digital image processor110.

FIGS. 8 and 12 illustrate implementing of a particular geolocalizabletonescale. For the construction of the tonescale 142, suitable testtargets 102 are exposed, chemically processed and scanned by scanner104. The conversion 126 to reference scanner density 124 is performed,and the target is custom balanced such that the 20% gray reflector mapsto equal code values of 1644 in the balanced reference space 166.

The tonal properties of the aim reproduction 89 in FIG. 8 arerepresented by the geolocalizable tonescale, in CIE 1976 L* values orvisual densities of the reproduced image 96 in relation to the scene 82.Those skilled in the art will recognize that the aims 89 may beconverted to a standard RGB space, e.g., ISO Standard Status Adensities, if the spectral reflectances of the image dyes and thereflective base material are known. It is then straightforward toconstruct a one-dimensional lookup table (1D LUT) between the balancedreference scanner densities 166 and the ISO Standard Status A densities.If the chosen dye set represents a “real” photographic paper, e.g.,KODAK EDGE Generations Paper, this 1D LUT can represent the ISO StandardStatus A versus printing density aim of a new photographic paper foroptical printing according to the invention.

In the digital implementation other suitable practical or hypotheticaldye sets may be chosen. Examples of suitable dyes were given by Hunt (p.135-1.48). Based on the known spectral reflectances of the dyes and thebase material, it is straightforward to calculate CIE XYZ values for CIEStandard Illuminant D50 and to convert those values to ICC PCS 144according to ICC specifications (Specification ICC.1:2003-09, FileFormat for Color Profiles (Version 4.1.0)). Thus, in the first preferredembodiment, the tone reproduction curve according to the invention isimplemented as ICC input profile 168 between balanced reference scannerdensities 166 and ICC PCS 144. This transformation may include othermathematical operations, e.g., matrices or polynomials to simulate theinter-image effect of the photographic paper (Giorgianni and Madden), or3D LUTs to achieve the overall desired color reproduction.

Optionally, the image processing sequence may include abstract profiles176, Which implement different image looks in PCS, e.g., differentflavors of black-and white reproduction such as sepia, or imagesaturation levels. Examples of such looks are disclosed in U.S.Published Patent Application No. US2001/0053247 A1, filed by Sowinski etal., entitled “Plurality of picture appearance choices from a colorphotographic recording material intended for scanning”.

The modified PCS values 176 are mapped to device code values 180,referring to the particular device and media combination, using an ICCoutput profile 172. This step ensures that the desired visualreproduction according to the invention, encoded in PCS (144, 176), isreproduced in the final print. Device characterization and calibrationare preformed by procedures known to those of skill in the art, such asthose outlined by Giorgianni and Madden (Chapter 13). The transformation92 in FIG. 8 includes all image processing steps between elements 122and 180 according to FIGS. 10 and 12, although any scene-specificprocessing (130, 134, 136, 140) must be disabled in the design andverification of the overall system tonescale according to invention.

EXAMPLE 2

In another embodiment, the image is captured using a digital camera,e.g., Kodak DX 6490, and printed on a Kodak Picture Maker® kiosk onthermal paper. For smooth skin tone reproduction on a 4×6 inch printwithout visible digital artifacts the sensor must at least have aresolution of 2 Megapixels, preferably above 3 Megapixels. Higher sensorresolutions are required for larger size prints. FIG. 13 describes theelements of the digital camera 52 which are necessary for practicing theinvention. The digital camera 52 includes an electronic display asoptical viewfinder for composing a scene (not shown), a 10:1 zoom lens184 controlled by a zoom lens driver (not shown) which is in turncontrolled by a processor 198. The zoom lens 184 includes an adjustableaperture and shutter (labeled as exposure and focus control 188) forfocusing light from a scene onto an image sensor 188. The camera mayalso include a flash unit 190.

The image sensor 188 is in this case a single-chip color charge-coupleddevice (CCD), using the well-known Bayer color filter pattern, but mayalso be a CMOS sensor or any other suitable sensor. When the userdepresses a shutter button (not shown), the image is captured using theimage sensor 188. The analog output signal from the image sensor 188 isconverted to digital data by an analog-to-digital (A/D) converter 192.The digital data passed to an image buffer 194 for temporary storage andprocessed by a processor 198 controlled by firmware stored in areprogrammable memory 196, such as a Flash EPROM. The regionalpreference configuration that would include the tonescalecharacteristics described in the invention can be applied at this stagein the camera. The processed digital image file is provided to a memorycard interface 200 which stores the digital image file on the removablememory card 54, in this case a SmartMedia™ card (a special form of SSFDCcard compatible with the PMCIA Standard and trademarked to Toshiba) orinternal memory 206.

The processor 198 performs color interpolation followed by color andtone correction, in order to produce rendered sRGB image data. The tonereproduction curves according to the present invention are implementedas part of this processing sequence. Other image enhancement algorithmssuch as noise reduction, sharpening and adaptive tone scale modificationcan also be applied at this stage within the camera and may bespecifically configured to provide optimum regional skin reproduction inconjunction with the tone scale of the present invention.

This processing is shown in FIG. 14. The processor 198 can includeinternal buffer memory to store a portion of the image, or to store oneor more images. Alternatively, the processor 198 can use a separateexternal memory (not shown), such as DRAM memory. The rendered sRGBimage data is then JPEG compressed and stored as a JPEG image file onthe removable memory card 54. For smooth appearance of human faces theJPEG compression ratio must be such that the file size for a 4×6 inchprint does not fall below 200 kB. Lower compression ratios are requiredto produce larger prints, which are free of digital artifacts. Theprocessor 198 also provides a lower resolution or “thumbnail” size imagedata to a color image display 204, such as a color liquid crystaldisplay (LCD), which displays the captured image for the user to review.A camera user interface 202 including a series of user buttons and acapture/review mode switch is used to control the digital camera 52.This GUI is controlled by the user interface portion of the firmwarestored in the Flash EPROM 196. This interface can be used to customizesettings and image processing parameters of the camera, as will bediscussed later in connection with FIGS. 15-16 c. Any changes to camerasettings may be loaded into the reprogrammable Flash EPROM 196. Theprocess of storing firmware code in an EPROM and of erasing firmwarecode from an EPROM is well known in the art, and need not be discussedin detail.

After a series of images has been taken by the digital camera 52 andstored on the removable memory card 54 the memory card is inserted intoKodak Picture Maker® kiosk 64 and printed on Kodak EKTATHERM thermalpaper XTRALIFE™ lamination 66. This printer and media combination wascharacterized according to standard procedures such that the printer isable to reproduce the tonal information encoded in sRGB. The user mayselect any additional enhancement operations that are normally offeredby a kiosk, e.g., zoom and crop operations, redeye removal andadditional sharpening and color and tone adjustment if desired.

FIG. 14 shows the steps carried out in the processor as far as they arerelevant for this invention. Other steps, such as noise reduction,sharpening and redeye removal may also be included. As a first step, thefully populated R, G and B planes are generated by CFA interpolation 212from the sparse set of ROB code values captured by the sensor 210. Next,a white balance algorithm 214 is applied to normalize the RGB valuessuch that a 100% white diffuser has a predetermined set of equal RGBcode values. An example of a suitable algorithm was disclosed by Gindeleet al. (US Patent Application No. 2003/0280650A1 “Method for AutomaticWhite Balance of Digital Images”). As discussed in connection with thescene balance algorithm 130 in FIG. 10, this white balance algorithm 214will have some distribution of errors. Averaged over a large number ofscenes the algorithm is able to meet the predetermined aim. It may bethe case that the this specification produces on average good skin tonerenditions in one geographic region, but that a different skin tonerendition is preferred in another geographic region. The appropriatecolor and density balance offset to produce good skin tone renditions inthe second region may be supplied to the white balance algorithm 214 viathe regional parameter set 1 (reference number 216), so that the balanceof the overall population of images is shifted by the specified amount.

At this point it is advantageous to convert the white balanced cameraRGB code values to a set of RGB values with standard or commonly usedprimaries, for example those defined in Recommendation ITU-R BT.709,which were also selected for the sRGB color space, or the primariesdefined by Spaulding et. al. (K. E. Spaulding, G. J. Woolfe, and E. J.Giorgianni, “Reference Input/Output Medium Metric RGB Color Encodings(RIMM/ROMM RGB)”, Proc. PICS 2000, pp. 155-163 (2000)). The relationshipbetween scene luminance and RGB code values in the reference RGB space220 may be linear, logarithmic or follow any other predefined functionalrelationship. For computational efficiency the transformation frombalanced camera RGB values is accomplished by a matrix and 1D LUT 218.

It is often the case that the preferred color and density balance ofscenes containing people is different from scenic images without people.For example, a lighter balance may be preferred for scenes containingpeople, but this may make scenic images appear too washed out. This canbe addressed by including a skin detection algorithm 222 in the imageprocessing sequence in order to apply different balances to both typesof scenes. A suitable algorithm is disclosed in Dupin. This algorithmuses an aim density for the preferred rendition of skin tones, whichagain may be customized by geographic region. The regional parameter 2(reference number 225) determines the magnitude of the brightnessadjustment performed by the algorithm 224.

Other image enhancement algorithms adaptive tone scale modification 226can also be applied at this stage within the camera and may bespecifically configured to provide optimum regional skin reproduction inconjunction with the tone scale of the present invention. Suchalgorithms enhance highlight and shadow detail of scenes with a dynamicrange too large to be accommodated by the output color encoding in sRGB234. Suitable algorithms are disclosed in U.S. Pat. No. 6,285,798 B1, toLee, entitled “Automatic tone adjustment by contrast gain-control onedges”.

Those skilled in the art recognize that the aim CIELAB values of thereproduction can be converted to PCS or sRGB using the appropriatedefinition of those color encodings. Thus it is straightforward toconstruct a 1D LUT between the RGB code values of balanced neutralcolors in the reference RGB space 230 and the corresponding sRGB codevalues representing the tone reproduction 232 according to theinvention. If the primaries of the reference RGB space 220 differ fromthose of the sRGB encoding, an additional matrix may be included. Thepreferred conversion method is therefore a matrix/1D LUT combination234.

It is also possible to follow the transform the balanced reference RGBvalues 230 to sRGB using the concatenation of ICC profiles shown in FIG.12. In the case of the digital camera part 162 are replaced withbalanced reference RGB code values 230, and output device code values180 represent sRGB code values 234.

The regional customization parameters 216 and 256 can be preloaded froma database to Flash EPROM 196 for a given geographic region or countryin manufacturing if the destination of the camera is known.Alternatively, the camera may be shipped with standard settings, butseveral alternative settings are stored in the internal memory 206 ofthe camera or on Flash EPROM 196. The user can alter the settings fromthe camera user interface 202. The high level menu shown in FIG. 15 canbe part of a set of menus that the user may display on the camera colordisplay 204 to customize the function of the camera 52. Such menus arecommon in digital cameras, and they allow the user to customize manyfunctions such time and date stamps, zone weighting of autofocus and theexposure control 188 and many others. This first level of the menu 240contains a title 242, graphic icons 244 and verbal descriptions 246 ofthe categories that can be modified, e.g., country, color balance, skinpreference. The selected category is shown in a different color or withother highlighting 248, and at selection the submenus shown 250, 258 and260 in FIGS. 16 a-c appear. The submenus 250, 258 and 260 contain atitle 252 and verbal descriptions 254 of the available settings. Moresettings than shown on the display 204 may be available and can beaccessed by scrolling down the menu. The selected item is denoted by acheck mark 256. Scrolling to the left selects this item and takes theuser to the previous high level menu 240. The new settings are loaded toFlash EPROM 196, which is accessed by the processor 198, when newcaptured images are processed.

Any text in FIGS. 15-16 c can be displayed in different languages.Alternatively, a digital camera can lack regional customization and thesRGB images can be saved to the removable memory card 54 without anyregional modifications. In this case, a special software packageresiding on the host computer 70 can be provided that recognizes thecamera model and then provides for regional customization, as shown inFIGS. 15, 16 a-c, and performs additional processing to produce sRGBimages 234 according to the selected preferences. This can be done whenthe images are imported from the removable memory 54 to the hard disk ofthe computer 70. The user can select from a number of availablecountries and regions using the menu 152. This loads the recommendedsettings for color and density balance and skin preference, showing thecorresponding positions of the sliders 154 and shifts in numeric form158. The user may then either enter new numerical values 158 or move thesliders 154 to change the preferred shifts. The user may save the newsettings using radio button 162 or return to the previous settings bypressing the “Cancel” button 160. The new settings are communicated tothe digital image processor 110. An example of a suitable package is theKodak EasyShare software distributed with all digital cameras made byEastman Kodak Company.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A method implemented at least in part by a microprocessor-based unit,the method for providing image-processing parameters for an image, themethod comprising the steps of: acquiring information about a device,the device being an image-acquisition device that acquired or isacquiring the image or an output device with which the image is to bereproduced; providing a regional image processing parameter based atleast upon the information, the regional image processing parameterrelating to geographic location; and storing the regional imageprocessing parameter in a computer-readable storage medium.
 2. Themethod of claim 1, wherein the device is an image-acquisition device andthe information about the device is a device model.
 3. The method ofclaim 2, wherein the device is a camera and the information about thedevice is a camera model.
 4. The method of claim 1, wherein the regionalimage processing parameter relates to reproduction of skin tones.
 5. Acomputer-readable storage medium storing instructions configured tocause a microprocessor-based unit to implement a method for providingimage-processing parameters for an image, wherein the instructionscomprise: instructions for acquiring information about a device, thedevice being an image-acquisition device that acquired or is acquiringthe image or an output device with which the image is to be reproduced;instructions for providing a regional image processing parameter basedat least upon the information, the regional image processing parameterrelating to geographic location; and instructions for storing theregional image processing parameter in a computer-readable storagemedium.
 6. The computer-readable storage medium of claim 5, wherein thedevice is an image-acquisition device and the information about thedevice is a device model.
 7. The computer-readable storage medium ofclaim 6, wherein the device is a camera and the information about thedevice is a camera model.
 8. The computer-readable storage medium ofclaim 5, wherein the regional image processing parameter relates toreproduction of skin tones.
 9. A system comprising: amicroprocessor-based unit; and a computer readable storage mediumcommunicatively connected to the microprocessor-based unit and storinginstructions configured to cause the data processing system to implementa method for providing image-processing parameters for an image, whereinthe instructions comprise: instructions for acquiring information abouta device, the device being an image-acquisition device that acquired oris acquiring the image or an output device with which the image is to bereproduced; instructions for providing a regional image processingparameter based at least upon the information, the regional imageprocessing parameter relating to geographic location; and instructionsfor storing the regional image processing parameter in acomputer-readable storage medium.
 10. The system of claim 9, wherein thedevice is an image-acquisition device and the information about thedevice is a device model.
 11. The system of claim 10, wherein the deviceis a camera and the information about the device is a camera model. 12.The system of claim 9, wherein the regional image processing parameterrelates to reproduction of skin tones.